1. Field of the Invention
The invention relates to a ring designed to be clamped around a shaft of a hydraulic machine for the purpose of forming a hydrostatic or hydrodynamic bearing. The invention also relates to a hydraulic machine including, inter alia, such a ring. Finally, the invention relates to a method of mounting such a ring on a hydraulic machine shaft for the purpose of forming a portion of a hydrostatic or hydrodynamic bearing.
2. Brief Description of the Related Art
A hydraulic machine comprises a rotary portion, such as a wheel or “runner” of a turbine or of a turbine pump, which wheel is designed to have a forced flow of water pass through it. Such a forced flow is a driving flow when the machine operates as a turbine, and a driven flow when the machine operates as a pump. In such a machine, a radial hydrostatic or hydrodynamic bearing can be provided around a shaft that supports the wheel, with the function of taking up the radial forces to which said shaft is subjected. The radially inner portion of such a bearing is sometimes constituted by a metal ring that forms an interference-fitted band in that it is clamped around the shaft. Such a ring is generally formed integrally as a single piece, i.e. it extends in one piece over 360° around the shaft, thereby ensuring continuity for its radially outer surface that constitutes the radially inner surface of the bearing. The fact that the ring is in one piece is a source of design and assembly constraints.
Multi-part rings made of metal could be devised, such rings being assembled around the shaft by welding or by mechanical means. In order to ensure good continuity and circularity that is as exact as possible for the radially outer surface of such a ring, rectification machining would need to be effected on the ring, once said ring has been assembled around the shaft, after the orifices for passing the assembly means such as bolts have been filled. In practice, such machining operations, to be performed on site would be lengthy and difficult, even though they would not guarantee continuity and circularity for the outside surface of the ring.
In addition, rings made of ceramic exist that cannot be assembled by welding and with which use of mechanical assembly means would induce discontinuities in the material of their outside surfaces. That is why such rings are always made integrally as a single piece, and must therefore be inserted over a hydraulic machine shaft via one end of that shaft which must have transverse dimensions less than the dimensions of the central bore of the ring. This can be problematic when a shaft is provided with lower and upper ends respectively of the “base” and of the “head” type that are enlarged so as to co-operate respectively with a turbine wheel and/or with the inlet shaft of an alternator.